1. Field of the Invention
The present invention relates to a two-component developer unit of a dry electrophotographic image forming apparatus, and more particularly, to a two-component developer unit of a dry electrophotographic image forming apparatus having a rectifier capable of solving nonuniformity of a developing density caused by a lack of a developer.
2. Description of the Related Art
Recently, a dry electrophotographic image forming apparatus, e.g., a laser printer, a facsimile using ordinary papers, a digital copier, etc., is in widespread use.
A two-component developing method is used in a dry electrophotographic image forming apparatus. In the two-component developing method, a developer is formed by agitating a mixture of nonmagnetic toner and a magnetic powder carrier and then producing frictional static electricity among toner particles so that the toner particles are adsorbed to the magnetic powder carrier. Next, the developer is adsorbed onto a developer magnet roller having a developer sleeve and rotated on a fixed magnetic pole, and then transferred to a photoreceptor. Next, a magnetic brush formed on the photoreceptor develops a latent electrostatic image on the photoreceptor.
FIG. 1 is a schematic cross-sectional view of a conventional two-component developer unit used in a laser printer. Referring to FIG. 1, in the laser printer, a printed surface of a printing paper 17 faces downward via a C-type transfer path through which the printing paper 17 is fed upward from a paper cassette (not shown) disposed under the laser printer. Thus, a laser beam 5 that is modulated to an image signal is horizontally incident on an exposure point of a photoreceptor 1, which has been charged with a predetermined potential by an erasing roller 24. Thus, the photoreceptor 1 is exposed to the laser beam, and then a latent electrostatic image is recorded on the photoreceptor 1. The conventional two-component developer unit includes a blade installing portion 8b, a toner density sensor 12, another gear 19 of the separator 20, a lamp guide 22 of the erase lamp 25, and another gear 25 rotating the erasing roller 24.
The photoreceptor 1 rotates clockwise as shown with an arrow so that the latent electrostatic image is developed by a developer unit A at a developing point having an angle of 70° with the exposure point with respect to a center of the photoreceptor 1. As a result, a toner image is formed on the photoreceptor 1, and the photoreceptor 1 faces the printing paper 17, which is fed to a transfer point having an angle of 100° with the developing point with respect to the center of the photoreceptor 1 and is supplied with a transfer voltage from a transfer roller 18 so as to transfer the toner image onto the printing paper 17.
The printing paper 17 is obliquely fed to the laser printer, fixed by a fixing unit (not shown), and discharged upward.
Accordingly, the erasing roller 24, an erasing lamp 23, a cleaning blade 21, and a separator 20 shown in FIG. 1 are disposed over the laser beam 5. Also, the developer unit A, which can be put into and pull out of a housing 2 like a cartridge, is disposed under the laser beam 5.
The developer unit A includes a toner feeding unit 3 having a toner feeding roller 4 and a toner agitating roller 6. Toner drops from a toner feeding outlet 3a underneath the toner feeding roller 4, is mixed with a developer 16 containing a carrier and the toner circulating in an inside of the housing 2, agitated, and charged with another predetermined potential. Here, a developer transfer roller 10 and an agitating paddle 11 mix and agitate the carrier and the toner and the developer 16.
FIG. 2 is a left side view and a front view of the developer transfer roller 10 used in a prior art two-component developer unit and a present invention developer unit. Referring to FIG. 2, the developer transfer roller 10 has a drive shaft 10c at its both ends, which rotates the developer transfer roller 10, and a plurality of transfer paddles 10a which are formed by cutting end portions of circular plates. The transfer paddles 10a slant with respect to the drive shaft 10c and disposed to be spaced apart from each other around a roller shaft 10b, which connects the transfer paddles 10a. 
Accordingly, if the developer transfer roller 10 rotates one time, the transfer paddles 10a operate as wings so as to agitate and transfer the developer 16 in an axial direction and a circumferential direction of the developer transfer roller 10. Thus, the developer 16 transferred in the circumferential direction of the developer transfer roller 10 creates a two-time peak whenever the developer transfer roller 10 rotates one time.
In the above-described structure, the amount of the developer 16 adsorbed onto a developer magnet roller 7 is pulsated in a circumferential direction of the developer magnet roller 7. When the developer 16 having a non-uniform thickness reaches the developing point, a supply of the toner is excessive or short depending on the non-uniform thickness of the developer 16 on the developer magnet roller 7. Thus, an amount of the toner attached to the latent electrostatic image varies and an image is shaded in a horizontal direction. As a result, the image becomes non-uniform, and thus a quality of the image deteriorates.
Therefore, a developer blade 8 having a flat shape is installed between the developer transfer roller 10 and the photoreceptor 1. A blade tip 8a is spaced apart from the developer magnet roller 7 so as to control the thickness of the developer 16 to a predetermined height. The blade tip 8a removes pulsated portions of the developer 16 from the developer magnet roller 7.
However, according to the above-described structure, since the developer magnet roller 7 is placed over the developer transfer roller 10, the developer magnet roller 7 serves to draw up the transferred developer 16. In this structure, a portion for collecting the sufficient amount of the developer 16 may not be formed around the developer blade 8. Thus, the intensity of the image becomes non-uniform and the image quality deteriorates.
Accordingly, to solve the above problems, a distance between the developer magnet roller 7 and the developer blade 8 is increased even though the portion collecting the developer is not included around the developer blade 8, a region, which is called an “ear-type collection portion”, is formed adjacent to the developing point so as to gather the sufficient amount of the developer 16 between the photoreceptor 1 and the developer magnet roller 7.
However, in the above-described structure, since the developer 16 gathered in the ear-type collection portion violently contacts the photoreceptor 1, an overweight load is given to the developer 16 and the photoreceptor 1, the toner adheres to the carrier, and the surface of the photoreceptor 1 is worn out. As a result, a life span of the developer 16 and the photoreceptor 1 is shortened. Also, since a torque of a drive motor rotating the photoreceptor 1 is increased, the drive motor has to be large-sized.